Publication Date

Fall 2012

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Dr. James T. Harvey


bacterial indicator, harbor seals, marine mammal health, Vibrio, virulence

Subject Areas

Ecology; Microbiology; Veterinary medicine


Given their coastal site fidelity and opportunistic foraging behavior, harbor seals (Phoca vitulina) may serve as sentinels for coastal ecosystem health. Seals using urbanized coastal habitat can acquire enteric bacteria, including Vibrio, that may affect their health. To understand Vibrio dynamics in seals, demographic and environmental factors were tested for predicting potentially virulent Vibrio in free-ranging and stranded Pacific harbor seals (P. v. richardii) off the coast of California. Vibrio prevalence did not vary with season and was greater in free-ranging seals (29%, n = 319) compared with stranded seals (17%, n = 189). Of the factors tested, location, turbidity, and/or salinity best predicted Vibrio prevalence in free-ranging seals. The relationship of environmental factors with Vibrio prevalence differed by location and may be related to oceanographic or terrestrial contributions to water quality. Vibrio parahaemolyticus, V. alginolyticus, and V. cholerae were observed in seals with V. cholerae found almost exclusively in stranded pups and yearlings. Additionally, virulence genes (trh and tdh) were detected in Vibrio parahaemolyticus isolates. Vibrio cholerae isolates lacked targeted virulence genes, but were hemolytic. Three out of four stranded pups with V. parahaemolyticus (trh+, and/or tdh+) died in rehabilitation, but the role of Vibrio in causing mortality is unclear, and Vibrio expression of virulence genes should be investigated. Considering that humans share the environment and food resources with seals, potentially virulent Vibrio observed in seals also may be of concern to human health.